Axial roller bearings are provided in different applications to carry axial loads. In some applications, axial roller bearings are provided with races having a convex rolling element contact surface in cross section, such as shown in U.S. Pat. No. 5,975,763. This design allows the races to deform with increasing load so that the contact between the needle rollers and the races is proportional to the applied load, allowing the load bearing capacity of the bearing to proportionately increase under an applied load. This arrangement is indicated as increasing bearing life and is said to reduce noise and optimize efficiency under variable load conditions. However, it has been found that this arrangement can create high contact pressures due to the reduced contact area, which results in poor formation of the lubrication film.
In certain applications, such as torque converter axial bearings, the load is not applied at a constant radial position due to expansion of the torque converter. These conditions result in the axial load contact position shifting radially outwardly on the bearing ring, thereby placing a higher axial load on radially outer regions of the rollers which can, in effect, pinch the rollers at their outer ends. This may lead to premature spalling failure of the axial roller bearing. The use of an additional flat washer as a thrust surface, such as in U.S. Pat. No. 5,918,987, does not address these problematic effects of edge loading.
It would therefore be desirable to provide an axial roller bearing which addresses the problem of edge loading and other drawbacks of the prior art.